The present invention relates to water heaters and boilers in general, and in particular to water heaters and boilers which incorporate sediment agitating apparatus.
Water heaters are widely used in both domestic and industrial settings. Hot water is used in many cleaning applications from dishwashers to clothes washer to showers. Hot water is also used to control the temperature of many industrial processes, and for space heating within homes and factories. Hot water is also has important recreational uses in pools, spas, and hot tubs. However, water as typically found in industrial and domestic settings is not a pure substance, and contains to varying degrees dissolved and suspended minerals. As a result, it is often recommended that water heaters be cleaned or flushed out periodically to remove sediments that tend to accumulate within the water heater tank, particularly on the bottom of the tank.
The sediments which accumulate within water heaters have many sources. Sand and silt often accompany water obtained from wells, and even where water is supplied through city mains. Particles of rust and other debris may be entrained in well water or water supplied from city mains. Various chemical processes may result in the precipitation of particles within the hot water tank. Certain forms of water hardness, including lime scale, may be precipitated when the water is heated. Change in temperature and/or the availability of oxygen can result of the precipitation of minerals such as iron. The typical hot water tank can be an ideal system for precipitating these various contaminants because of the long periods of quiescence where little or no mixing occurs within the tank.
The effects of minerals precipitating and accumulating on to the bottom of a hot water tank are highly undesirable, particularly if the water within the tank is heated by an oil or gas flame. The accumulation of sediments on the bottom of the tank reduces water heater efficiency by reducing heat transfer. More serious than the mere loss of water heater efficiency is the greater temperature gradient which results because the sediments insulate the water heater bottom from the water contained within the tank. Because of the insulating effect of sediments within the tank, a larger thermal gradient is necessary to transfer heat through the tank bottom and the insulating layer of sediments. Because the water within the tank is insulated from the tank bottom, combustion gases are able to raise the tank bottom material to a higher temperature than would otherwise be the case. This higher temperature results in greater thermal expansion of the tank bottom and greater thermal cycling. If the temperature of the tank bottom is raised to a sufficiently high temperature, the material properties of the steel used to form the tank bottom can be altered so as to reduce strength and durability. Increasing the temperature of the tank bottom leads to the breakdown of the protective glass lining of the water heater. Thus the insulating effect of sediments which build up on the bottom of the water tank produces increased thermal cycling and loss of material properties, break down in the glass protective coating, and sometimes in aerobic bacteria, which can contribute to tank corrosion. These factors can eventually lead to leaking of the water tank, which requires replacement of the water heater.
What is needed is a water heater with active means for preventing the buildup of sediments on the bottom of the water tank.